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  <script>
    //初始值
    let num1 = 3
    let num2 = 7
    //  1.申明一个中间变量
    let num3
    //   2.把num1的值赋给中间变量
    num3 = num1
    //   3.把num2的值赋值给num1
    num1 = num2
    //   4.把中间变量的值赋值给num2
    num2 = num3
    // 5.输出=
    console.log(num1, num2);
  </script>
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